The multiplicity of controls to which the driver of a modern vehicle has access is such that numerous interfaces are developed allowing activation of the functions without having to look at the control or his hands. The user relies on digital feel alone to control a function and can thus keep his eyes concentrated on the road. Among other digital interfaces, directional knobs placed at the central console between the front seats now concentrate the activation of many controls, in particular the navigation system, the radio, the telephone and all of the telematics functions, as well as control of the ventilation and air-conditioning. To select a function, the user, by means of the knob, directs a cursor on a monitoring screen. Once the desired function has been displayed, the user validates his choice. To do this, and on the basis of experience developed in the field of computers and Internet navigation, different directional knobs have been developed for the motor vehicle environment. The first could only turn and pushbuttons situated around the knob permitted validation of the functions. For more pleasant and more accurate use, the rotation of the knob produces a cyclic force felt by the user.
Subsequently, the peripheral buttons were removed and replaced by extra functions of the directional knob. With the most recent models the user can navigate in menus offered on the monitoring screen by displacing the knob towards the front or the rear, or from left to right, he can still as before, turn the knob on itself and lastly, to validate his choice the user must now press on the knob which acts like a computer keyboard key. Differently from the levers and joystick of videogames, the displacements of the directional knobs for vehicles have very small amplitudes, limited to a few millimeters. Moreover, the displacements must be sure and precise so that the user, concentrated on the driving of the vehicle, easily selects and validates the function which he is seeking. Thus, without any operation, the knob returns by itself into a neutral position, it has no perceptible operating play which would be very unpleasant for the user and its displacements are always accompanied by return forces perceived by the user.
For direct and more rapid selection of certain functions, pushbuttons have sometimes been retained. They can be placed at the immediate periphery of the knob, and then constitute with the knob a general control unit. They can also be distributed in other locations accessible by the driver.
The visible part of the knobs operated by the driver is assembled with a system that can be mechanical comprising a lever, articulation joint, springs, or electronic with integrated circuit, angle sensors, stepped motor.
Mechanical systems are in particular presented in WO 2008/113593 A1, Eckert et al. proposing a mechanical knob pivoting front-rear and right-left simple in design but limited in displacement. A more complex mechanism is proposed by Torrents Gavalda in EP 1426991. It permits in addition the vertical depression of the knob but not the rotation proper of the knob. A third mechanism is proposed by Sato with U.S. Pat. No. 7,368,673 B2 in which the knob can in addition turn on itself. Contrarily to Eckert and to Torrents Gavalda, the front-rear and right-left displacements of the knob of Sato are due to translations and not to pivotings.
A known problem of the proposed mechanisms is associated with the fact that for the great majority of the time the knobs are not operated and remain in the neutral position. The pieces do not move and the contacts occur in the same places. Thus, ageing by non-use causes local deformations that can produce problems with accuracy and the perception of the user. To combat these deformations the use of noble materials and the reduction of forces are the two conventional routes for investigation by mechanics however, neither of these routes has up to now led to an acceptable solution. The strong materials are more costly and generally more difficult to work, while the reduction of forces causes a “limpness” in use and unacceptable inaccuracies with regard to the elastic return or the maintenance of the knob in the neutral position.
Today, electromechanical directional knobs more expensive than the mechanical knobs are fitted to almost all high range vehicles and constitute a considerable market differentiator. However, the functions of GPS, telephone, air conditioning, Hi-Fi, FM radio . . . are now present in virtually all vehicles and their control imposes the generalization of the directional knobs. The expansion of the market then requires control systems which are just as accurate reliable and pleasant to operate as those already in use but which, due to a modified design, are much less expensive.